The present invention relates to a system and method for controlling ignition timing in an internal combustion engine on the basis of the degree of engine knocking.
In general, in internal combustion engines, the pressure in combustion chambers (cylinder pressure) has a plurality of inherent resonant frequencies determined by the cylinder's dimensions (especially cylinder bore inner diameter). The damped pressure often causes the internal combustion engine to emit metallic rattling noise, i.e., knocking.
Various systems for the internal combustion engines have been proposed to eliminate knocking by controlling ignition timing.
Such systems are exemplified by Japanese Patent Applications Unexamined Open No. Sho. 54-142,425, Sho. 56-000,554, etc.
Such conventional systems extract accoustical signal components in a particular frequency band (above about 5 or 6 kilohertz) characteristic of knocking from among acoustical signals from a knocking sensor, such as a pressure sensitive sensor attached to a cylinder block or a washer for one of the spark plugs of the engine. The conventional systems then process the extracted signal, produce a detection signal corresponding to a combustion pressure vibration of the engine, determine the presence or absence of the occurrence of knocking by comparing the produced detection signal to a previously set reference level, and retard the ignition timing by a predetermined value of angle when the comparison indicates the presence of knocking.
However, there are drawbacks in the conventional systems disclosed in the above-identified documents as described below.
However, in systems such as described above, the relationship between the magnitude (level) of knocking and ignition timing changes with engine operating conditions which may at times lead to wasteful fuel consumption and to a reduction in engine output torque due to excessive retardation of the ignition timing when the knocking is relatively weak. In addition, the fixed rate of ignition retardation may not be sufficient to quickly suppress severe knocking. On the other hand, the fixed retardation will be excessive for weaking knocking, resulting in unnecessary loss of engine torque.